Newborn inbred strain 2 guinea pigs will be given heterologous antibodies specific for the idiotypic (id) determinants on the IgM molecules of the syngeneic L2C B cell leukemia and throughout the period of their immunological maturation. The L2C id suppressed young adult guinea pigs will be challenged with viable L2C leukemia cells and their susceptibility to the tumor will be studied. Guinea pigs which are resistant to the leukemia transplant will be studied to determine the molecular specificity of their immune response to the L2C tumor. Special attention will be given those guinea pigs in which anti-L2C id clones have been shown to be responsible for leukemia protection. The anti-L2C lymphoid clones will be evaluated for their capacity to render protection against the L2C leukemia in normal adult and tumor-bearing animals. The lambda chains of the L2C IgM excreted in the urines of leukemic guinea pigs will be analyzed chemically to determine the nature of their heterogeneity. In particular, it will be determined by amino acid analysis which lambda constant region gene(s) are being expressed by the L2C leukemia cell. The ecto-5'nucleotidase (5'N) activity of the various sublines of L2C cells will be determined and compared to normal guinea pig B lymphocytes present in the various lymphoid tissues. These studies will determine whether the level of 5'N activity is a stable plasma membrane phenotype among the L2C leukemia sublines.